[MUSIC PLAYING] Today I would like to share a new reference design from Texas Instruments targeted towards driving LED automotive daytime running lights. Modern daytime running lights can use upwards of 20 LEDs, which can require a high voltage to drive if configured in a series string. This reference design offers a single LED driver solution by driving parallel strings of LEDs and actively balancing the current between them to ensure equal brightness. Thermal foldback, PWM dimming modes, and current limiting are also features of this EMI-tested design.
Current balancing is achieved by an op-amp-based current mirror that splits the current from the LED driver between two strings. A balance accuracy of less than 1% can be achieved with this circuit. This reference design includes two brightness modes that can be selected based on which input is provided power. If the DRL input is powered the, LEDs will be driven at full brightness. Alternatively, if the position input is powered, the LEDs will be dimmed using the LED driver's internal PWM generator.
Linear thermal foldback protects the LEDs from overheating by reducing current linearly after a specified temperature is reached. The foldback starting point can be adjusted based on the gain of the non-inverting amplifier. Electromagnetic interference, or EMI, is a crucial aspect of automotive electronics design. The LED driver in this solution uses spread spectrum switching for improved EMI performance.
This reference design has been conducted and radiated emissions tested according to the CISPR25 Class 5 standard. For more information, visit the link below. Thanks for watching.

Description

February 28, 2018

Learn more about how this design is a dual string LED driver which implements an operational amplifier based circuit which balances the current in 2 LED rings.